Recently, research and development on secondary batteries have been actively conducted. Here, the secondary batteries, as batteries that can be charged and discharged, mean that they include conventional Ni/Cd batteries and Ni/MH batteries, and recent lithium ion batteries. Among the secondary batteries, the lithium ion battery has an advantage that the energy density is much higher than that of the conventional Ni/Cd battery and Ni/MH battery, and further, the lithium ion battery can be manufactured with a tendency of a small size so that it is used as a power source for a mobile apparatus. In addition, the usage range of the lithium ion battery extends as a power source for electric vehicles, so that the lithium ion battery attracts attention as a next generation energy storage medium.
Meanwhile, in the battery cell production process, an unknown discharge current that may occur in a manufactured battery cell is a type of failure that abnormally drops the voltage of the battery cell. The conventional technology for detecting the failure of a battery cell based on the voltage characteristic of the battery cell takes a long period of time from the completion of the production of the battery cell to the time point when the failure is detected so that the production rate of the battery cell is lowered.
Accordingly, the development of a new battery cell failure detection technique using an unknown discharge current, which can reduce the detection time compared to a conventional failure detection technique of a battery cell based on the voltage characteristic of a battery cell in order to increase the production speed of the battery cell, is required.